Phase modulation receiver



May 2, 1939. M. G. CROSBY PHASE MODULATION RECEIVER Filed Oct. 5, 1957 5 Sheets-Sheet l QEENGQ uzm mwt ii SQ QEEESE QM MURR/I Y 6'. CROSBY A TTORNEY.

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May 2, 1939- M. G. CROSBY PHASE MODULATION RECEIVER Filed Oct. 5, 1937 5 Sheets-Sheet 2 FREQUENC Y FREQUENCY l-Iullllllllllllll.

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May 2, 1939. M. G. CROSBY 215fi,375

PHASE MODULATION RECEIVER Filed Oct. 5, 1957 5 Sheets-Sheet 3 All PHASE MODUL47'ION 207 4500mm 206 Z 1 g g m 2/9 :w 7 m I I 55 2/3T\ T 55 211 4 +6 VAR/ABLE 4/2 GAP HOLDER INVENTOR.

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May 2,1939.

M. e. CROSBY PHASE MODULATION RECEIVER Filed Oct. 5, 1957 5 Sheets-Sheet 4 PHASE MODULATION ,4 F OUTPUT IAAAAAAA vIIIvv v A AFC RESULT/NG FROM PHASE M ODUL A Tl ON PHASE MODULATION WAVEENERGY bbbbbb in 1111111 1 INVEN TOR. ZJURRA Y 6. CROSBY ATTORNEY.

SE UNIT/0N A. F. OUTPUT T PHA MOD nnnn in 5 Sheets-Sheet 5 I n E n M. G. CROSBY PHASE MODULATION RECEIVER Filed 001;. 5, 1957 A. E RESULTING FROM PHASE MODUL A T/ON INVEN TOR. MURZY G. CROSBY ATTORNEIC May 2, 1939.

MODULA T/ON W4 l E ENERGY PHASE WAVE PHASE MOM/LA T/0/V Patented May 2, 1939 UNITED STATES PATENT OFFIQE PHASE. MODULATION RECEIVER Delaware Application October 5,

23 Claims.

In my United States application #165,056, filed September 22, 1937, I have described a receiver including a single crystal connected in an underneutralized circuit and in an over-neutralized circuit to obtain two filters of characteristics such as shown in my United States Patent #2,085,008, dated June 29, 1937. When phase modulated energy is passed by these filters it is converted to waves of amplitude modulation and the filter 10 outputs are so arranged that the modulation envelopes have a 180 relation so that a detector system coupled to said filter detects the amplitude modulations to render the signal while undesired amplitude modulations on the wave are substantially eliminated.

This disclosure describes a phase modulation receiver of the general type described above wherein I employ two crystal filters which are arranged so as to obtain the two desired characteristics described above which convert the phase modulation into two waves of amplitude modulation with a 180 relation between their modulation envelopes.

The fundamental idea of the type of reception utilized in this disclosure and the aforesaid application is described in my United States Patent #2,085,008, dated June 29, 1937, and in my United States application #138,117, filed April 21, 1937. The receiver about to be de- 30 scribed employs crystal filters connected in a manner different from the connections of the prior disclosures. This connection effects a simplification in the circuits required.

In describing my invention reference will be made to the attached drawings wherein Figures 1, 3, 4, 5, 6, 6a, and 7 each show a modification of my novel filter circuits for converting phase modulations on wave energy to characteristic amplitude modulations and demodulating the same, while Figures 2a to 2h are filter characteristic curves, reactance curves, and vector diagrams used to explain the operation of my converting circuits.

In Figure 1 is illustrated schematically a some- 4 what complete circuit arrangement of a wave converting and demodulating system including frequency control means. In the wave converting circuit of Figure 1, it will be noted that a shunt crystal filter arrangement is used. Modifications of the shunt arrangement of Figure 1 are illustrated in Figures 4 and 5. In Figure 3 the converting circuit is of the series crystal filter type. Figures 6, 7 and 8 illustrate modifications of the arrangement of Figure 3.

Figure 1 shows a complete embodiment of a 1937, Serial No. 167,344

receiver employing the principles about to be disclosed. Energy is fed from antenna l to unit 2 Where it may be amplified, and beat in a detector with oscillations from 0 so that it is converted to an intermediate frequency. The intermediate frequency energy is amplified and filtered in unit 3 and passed to the primary winding 6 of a transformer iii which winding is properly clamped by resistor 4 and tuned to pass a band of frequencies by condenser 8. The secondary winding l2 of transformer I0 is in a like manner damped by resistor 14 and tuned by condenser I6. In operation, the windings of I0 may be tuned to the mean frequency of the wave energy passed thereby or if necessary to make the transformer band pass characteristic square the primary and secondary windings may be detuned in either direction from said means frequency. The secondary winding 12 of transformer I0 feeds energy to two crystal filter cir- H cuits incorporating elements 17, 20, 2! and l8, l9, and 22. Resistors I! and i8 serve as isolating resistors to prevent reaction between the crystal filter circuits. One of the crystals, 2|, has an inductance, 20, shunted across it while the other crystal, 22, has a variable capacity, 19, shunted across it. The voltage drop across crystal 22 is fed to the control grid 26 of coupling or amplifier tube 23. The voltage drop across crystal 2| is fed to the control grid 25 of coupling or amplifier tube 24. Resistors R and R, which are properly bypassed by condensers as shown, furnish self-bias to the control grids 26 and 25 of tubes 23 and 2d, respectively.

The anode 28 is coupled to the primary winding 29 of a band pass transformer 30. The winding 29 is shunted by a damping resistance 3! and a tuning condenser 32. The anode 34 of tube 24 is coupled to the primary winding 36 of a transformer 38. The winding 36 is shunted by a damping resistance 39 and a tuning condenser 40. The secondary Winding 42 of transformer 30 is tuned by a condenser M and connected by a diode resistor 45 to the electrodes of a diode rectifier 47 while the secondary winding -9 of transformer 33 is tuned by a condenser 50 and connected by diode resistor 53 to the electrodes of a second diode rectifier 54. These diodes may be replaced by a double diode. The transformers 30 and 38 are also band pass transformers and may be tuned to the means frequency or substantially to the mean frequency as described in connection with transformer Ill. The diodes have resistors and 53, which are properly bypassed by condensers 56 and 57, connected in the manner shown which properly combines the converted phase modulation energy so that the audio outputs are accumulative.

Automatic frequency control energy is also taken from the drop across the diode resistors G5 and 53 and fed through time constant circuit comprising resistance 60 and condenser 62 and lead 68 to operate a reactance tube in a modulator M which controls the tuning of the high frequency oscillator O. The reactance tube 89 has its anode 84 coupled to the anode 93 of the oscillator tube 94 and also coupled through a phase shifting circuit including condenser 9|, .resistance 90, and condenser 88 to its grid 86. Resistor 89, which is properly bypassed, furnishes self-bias for tube 80. The grid 85 of 80 is coupled to the juncture of 88 and 99. Oscillator tube 94 has its grid 98, anode 93, and cathode I09 coupled in a frequency determining and stabilizing circuit 96 coupled by leads to the detector in 2. This reactance circuit and oscillator are as described in my copending application #165,056, filed September 22, 1937.

Audio frequency energy characteristic of the signal is taken from the drop across the diode resistors 45 and 53 through a blocking condenser 55 and fed to amplifier 59 by means of a potentiometer 10. Transformer 12 makesthe output available for utilization in jack 13.

The operation of this receiver can be more clearly understood by a reference to my Figures 2a to 2h inclusive, of the drawings. The reactance characteristic of crystal 22 with the capacity l9 across its holder is as shown in Figure 2b. Since the voltage is fed to this crystal circuit through resistor l8, which determines the current in the circuit, the drop across the crystal is inductive 0r capacitive depending on the frequency of the wave supplied by In and in accordance with the curve of Figure 2b. It can be seen that in the region where the side bands are disposedthe crystal is capacitive on both sides of the carrier frequency except for a small interval near the carrier frequency. Due to this fact, the phase of the side bands is shifted 90 with respect to the carrier as shown in Figures 20 and 2d in which the phase modulated wave of Figure 2c is converted to the amplitude modulated wave of Figure 2d by such a phase adjustment. The amplitude characteristic of such a filter is as shown in Figure 2a.

Crystal 2!, which is shunted by inductance 29 has a reactance-frequency characteristic as shown in Figure 2]. Thus, the phase of the side bands is shifted 90 lagging instead of leading as was the case with crystal 22. Consequently, the phase modulated wave of Figure 2c is converted to the amplitude modulated wave of Figure 2h. The amplitude characteristics of this filter are as shown in Figure 26. From an examination of Figures 2d and 271. it can be seen that the phases of the amplitude modulation envelopes resulting from the conversion of these two filters is out of phase. Consequently, the detection of this amplitude modulation and combination by the series connection of the diodes st and 54 and diode resistors 45 and 55 as shown in Figure 1 combines the phase modulation outputs additively. The resultant signal wave is impressed on 59 and appears for use in T3.

Amplitude modulation, both noise and signal, being received by this receiver balances out due to this connection of the diode resistors. This is because the amplitude modulations affect the.

filters in like manner and oppose and substantially cancel in the diode rectifiers. This is because the amplitude modulation is either converted to phase modulation which cannot be detected by the detectors, or because the amplitude modulation that is unconverted to phase modulation is balanced out by the push-pull con nection of the diode resistors.

Automatic frequency control energy is obtained by virtue of the fact that a diiferential voltage is available due to the amplitude characteristics of the filters. That is, on oposite sides of the carrier frequency the outputs of the two filters fall off with different rates in a manner which produces a differential amplitude characteristic.

This differential potential appears at A5 and 53 and acts through time control circuit 69, 62 to control the potential of the grid 82 of the reactance tube 80.

The automatic frequency control circuit is similar in some respects to that shown. in my United States Patent #2,065,565 dated December 29, 1936; Patent #2,085,008 dated December 29, 1936; application #124,967 filed February 10, 1937; application #136,578 filed April 13, 1937; and application #165,056 filed September 22, 1937. The oscillator O is of the grounded grid type and includes a tube 94 having its grid 98, anode 93, and cathode H19 coupled in afrequency stabilizing and determining regenerated circuit 96 as shown. The grid end of the circuit is grounded for radio frequency since the grid leak 99 is bypassed by a condenser. The reactance tube 89 has its anode 84 coupled to its grid 86 by coupling condenser 9!, resistance 99, and phase shifting condenser 83. Anode 84 is also coupled to the high potential end of the circuit 95, while the cathode of tube 80 is grounded by way of a. biasing resistance 89 and bypassing condenser in shunt to said resistance. The value of resistance 99 is high as compared to the reactance of condenser 88 for the frequency used so that the current through this circuit is largely resistive and is in phase with the voltage. However, the voltage drop through 88 leads the current by substantially 90 and the phase quadrature relation between the radio frequency potentials on 8G and 89 necessary for the reactive effect, is obtained.

The tube reactance shunts the circuit 96 and consequently the reactance tube controls, to some extent, the frequency of the oscillations produced in 96 and tube 94. This reactive eifect which may be considered inductive or capacitive, is in turn controlled by the potential supplied from the time control circuit iii], 62 to the grid 82 of reactance tube 80. The potential supplied to 82 is afunction of the mean frequency of the intermediate frequency energy supplied by 30 and 38 changing as the intermediate frequency drifts in either direction from this mean frequency. Such drift may be caused by the change in frequency of the received wave or the frequency of the oscillator O or both and results in a correcting change in the reactance reflected by the reactance tube 39 into the circuit 96 or a part thereof. Since the plate 86 is connected to the plate 93 and the grid 86 is excited by voltage displaced in phase relation to that in the circuit 96, the plate current int?! is likewise out of phase with the voltage of 93 and the control tube 89 looks like a reactance to the circuit 96. A reactance tube somewhat similar to the one described above has also been shown in my United States application #209,919 filed May 25, 1938.

Thus, shifts of a mean intermediate frequency act through 30 and 38, 41 and '54, 45 and 53 to produce potentials of a nature determined by the direction of said shift and of a magnitude determined by the extent of said shift and these potentials act through the time control circuit 60, 62. to produce characteristic reactive changes in tube which appear in circuit 86 to produce a correcting shift in the frequency of the oscillations produced by oscillator O and supplied to the detector in 2 for reducing the frequency of the received wave energy.

In describing and illustrating the modification in Figures 3, 4, 5, 6, '7, and 8 the elements between the reactance 8 and the aerial I will in the sake of simplicity, be omitted as will the frequency control circuits and oscillator between 45, 53 and the unit 2. Obviously one skilled in the art may add the same or equivalent elements to the converting circuits of the remaining figures.

In the circuit of Figure 3, as in Fig. 1, two separate crystals are utilized to produce the underand over-neutralized characteristics. One of these crystals, say )3, is fed neutralizing energy in the manner described in my copending application. The other crystal is used without neutralization, i. e., unneutralized. Intermediate frequency energy is fed to band pass tuned transformer H] which is properly damped by resistors 4 and M. The secondary windin i2 is grounded between its ends to provide neutralizing energy and to feed energy to the crystals Hi3 and HM. Crystal 33 has its holder capacity over-neutralized by neutralizing condenser Hi5 and feeds its energy to the control grid 26 of coupling and amplifier tube 23. Crystal I04 feeds its unneutralized energy directly to the control grid 25 of coupling and amplifier tube 24. The characteristic of the filter circuit at the output terminals of transformer 30 is therefore as indicated in Figure 2e this being an over-neutralized filter and the characteristics at the output of transformer 38 will be as indicated in Figure 2a, this being of the under-neutralized type. These two filters of characteristics as indicated in Figure 2e and 2a will, as pointed out in detail hereinbefore, have reactance characteristics as indicated in Figures 2i and 2b respectively, and will convert the phase modulations to characteristic amplitude modulations, the envelopes of which will be of opposed phase in the detector inputs.

Resistors H4 and H5 produce self-biasing potentials for the amplifier or coupling tubes 23 and 24 and may be bypassed as shown, or left unbypassed so that inverse feedback results. This feedback tends to reduce the distortion in these coupling tubes. The detecting system comprising tubes 4'! and 54, which may be in. the same envelope, and diode resistors 45 and 53 operate in the same manner as the circuit of Figure 1.

Figure 4 is somewhat similar to the prior figures in circuit arrangement and is quite similar to the prior figures iii-operation. In Figure 4 wave energy to be converted is impressed on resistor 2? and from 26]! to the control grids 205 and 206 of two amplifying and coupling tubes 2G2 and 203. The anodes Ziil and 29'! of these tubes are connected as shown to damped tuned transformers 208 and 2H). Two crystals 2|6 and Eli are connected as shown in shunt to the tuning condensers 2l2 and 2E3 for the secondary windings of transformers 263 and 2m respectively. The secondary winding of transformer 208 feeds energy to the diode rectifier 2H3 while the secondary winding of transformer 2H] feeds energy to the diode rectifier 219.

The crystals 216 and 2H are ground so that their points of maximum energy transfer, which would be at their carrier frequencies, coincide. One of them is put in a variable airgap holder to aid in synchronizing the carrier frequencies. This same expedient may also be applied in the circuit of Figure 3. Intermediate frequency energy is applied to coupling tubes 282 and 203 via potentiometer 20!. secondary 209tuned so that the holder capacity for crystal 256 is not resonated. That is, condenser 2l2 is tuned so that the secondary is inductive and the crystal holder capacity is not tuned out. Condenser N3 of transformer m is then tuned so that this transformer secondary 2i! is capacitive. With this arrangement of an inductive feed to one of the crystals, say 2H, and a capacitive feed to the other crystal M8 the separate filter characteristics resulting are as shown in Figures 2a and 26. Consequently, the proper converting systems for the back-to-back detection of phase modulation is effected by this filter system in the same manner as is effected in the other receivers. The manner in which this conversion takes place and in which the characteristic amplitude modulation envelopes are caused to be out of phase will be clear to one skilled in the art from the foregoing explanation of the previous figures and a repetition of such description is thought unnecessary here.

In the circuit of Figure 5, a simplified arrangement somewhat similar to the arrangement of Figure 1 is shown. In Figure 5 the tuned circuits 300 and 3| I] are placed across the crystal holders so as to complete the direct current paths for the diodes and thereby allow the elimination of the coupling tubes used for overor under-neutralizing the crystal holders of the prior figures. One of these tuned circuits is tuned to the capacitive side of resonance and the other tuned circuit is tuned to the inductive side of resonance to thereby produce either a capacitive or inductive effect just as though only capacity or inductance were present singly as in Figure 1. The remaining portions of this converting circuit is similar in many respects to the circuit of Figure l, and corresponding ref erence numerals indicate corresponding parts. Here again, it is thought the operation of the circuit of Figure 5 will be clear to one skilled in the art and the specification will not be burdened with a repetition of such description here.

In the above circuits of Figures 1 and 5 the feeding resistors l1, l8 may be unbalanced to take care of differences encountered in the amplitude characteristics of the two crystal filters. Variable airgap crystal holders may be used to aid in synchronizing the resonant frequency of the two crystals. Condenser I9 and inductance 20 as well as tuned circuit 300 and tuned circuit 3!!! may also be varied to synchronize the carrier frequencies of the two crystal filter circuits.

In the converting circuits or filters of the present invention as illustrated in the prior figures, it is obviously an advantage to keep the same of low impedance to thereby increase the selectivity of the crystals used therein for converting phase modulated waves to corresponding amplitude modulated waves. Although in the prior figures, such as for example, 3, the transformer windings are of high impedance so that crystals are fed by and are in high impedance circuits, if

Transformer 2&6 has itscare is taken in the choice of crystals and in the grinding of the same sufficient selectivity is obtained. The extent or degree of carrier exhaltation accomplished in the circuits and filters depends upon the selectivity of the circuit. A highly selective circuit exhalts the carrier to an extent greater than does a circuit of low selectivity. In Figure 6 I have shown a circuit arrangement somewhat similar to the arrangement of Figure 3. In Figure 6, however, the transformer in is of the step-down type and steps the high impedance input primary winding to a low impedance secondary winding i6 feeding the crystals E93 and Hi l While the transformers 3i? and 38 are of the step-up impedance type and step the impedance back up again in the secondary windings which feed the diode rectifiers "1 and 5 Figure 6 therefore in this respect differs from the arrangement of Figure 3 and also differs from the arrangement of Figure 3 in that the coupling and amplifying tubes of Figure 3 have been eliminated in Figure 6. In Figure 6 the crystals I83 and H34 are in low impedance circuits and this improves their selectivity in a manner known to the art. The reason that for this improvement in selectivity is that the low impedance windings I6, 29, and 36 more nearly match the impedance of the crystals m3 and Hi l, which impedances are quite low at resonance.

Another improvement increases the selectivity of the crystal filters in all of the modifications is the use of silvered, plated, or evaporated electrodes which have been deposited on the surfaces of the crystal. By clamping the crystals at nodal points of vibration, the damping effect of the airgap holder is eliminated and a more selective filter results. The clamping means also serves as the electrodes for connecting the crystals in the circuit. Deposited electrode crystals are known in the art. They were first used by the Bell Laboratories, and have been described in the March 1933 issue of the Bell Laboratories Record, page 200.

In the modification of Figure '7, which is similar to the modification of Figure 3, a neutralizing condenser 105' has been provided for, feeding neutralizing energy to the output electrode of crystal Hi l also. I have found that it is advantageous to provide a neutralizing condenser for the crystal holders in both the overand under-neutralized circuits. In the modification as shown in Figure 3 the neutralizing condenser m5 is provided for the holder of crystal 583 only and the holder of crystal i 04 is left unneutralized. The arrangement of Figure 3 runs satisfactorily but I have found that an increased degree of carrier exhaltation is obtained if the degree of off-neutralization is reduced. In order to reduce the degree of ofi-neutralization neutralizing condensers I and H35 are provided as in Figure 7, for both the underand over-neutralized circuits. This permits me to control at will the degree of off-neutralization of the circuits. The arrangement of Figure 7 is in other respects substantially the same as the arrangement of Figure 3.

The modification of Figure 8, which is otherwise similar to the modification of Figure 6, described above, also includes means for varying the degree of overor under-neutralization of each crystal and this is accomplished as in Figure 7 by providing an additional variable capacity I05 connected as shown.

The modifications in Figures 6, '7, and 8 operate substantially as described heretofore in connection with Figures 1 and 3 to convert the phase modulations on the wave energy intocorresponding amplitude modulated wave energies with modulation envelopes of opposed phase so that when they are rectified as shown, the amplitude variations caused by the phase modulations add and are utilized while unwanted amplitude modulations on the received wave cancel.

Although I have described all of the modifications as being adapted to the reception of phase modulated Wave energy and including means for eliminating undesired amplitude modulations on the wave energy, it is to be understood that the same circuits may be used as frequency discriminator circuits to obtain in the manner described frequency controlling potentials in the output which are characteristics of changes in the mean frequency of the intermediate frequency energy resulting from any cause whatever such as shifts in the frequency or the received Wave or frequency of the local oscillator beat with the received wave. Moreover, these circuits when so used are selective enough to hold the intermediate frequency carrier in tune with the sharpest bandpass filters now available. When so used the receiver may be for frequency control purposes only or for the same with the reception of amplitude modulated wave energy. In the latter case means is provided preceding the detectors or following the detectors for reversing the polarity of the side bands of the detected energy relative to the polarity of the combination used in the circuits shown.

The tube electrodes may be charged and/or heated by conventional means and to simplify the drawings and description such circuits have been omitted.

I claim:

1. In a filter system for filtering modulated wave energy, a reactance energized by said modulated wave energy, an impedance, a series circuit including said impedance and reactance and output terminals, a piezo electric crystal in a holder connected in shunt to said output terminals said crystal in its holder being parallel resonate at substantially the mean frequency of the modulated wave energy, and a utilization circuit connected to said output terminals.

2. In a filter system for filtering modulated wave energy, a reactance tuned substantially to the mean frequency of said wave energy and energized by said modulated Wave energy, an impedance, a series circuit including said impedance and reactance and output terminals, a piezo electric crystal in a holder connected in shunt to said output terminals said crystal in its holder being parallel resonate at substantially the mean frequency of the modulated wave energy, and a reactance shunting said crystal holder to supplement the effect of the crystal holder in said circuit.

3. In a filter system for filtering modulated wave energy, a tuned reactance energized by said modulated wave energy, an impedance, a series circuit including said impedance and reactance and output terminals, a piezo electric crystal in a holder connected in shunt to said output terminals said crystal in its holder being parallel resonate at substantially the mean frequency of the modulated wave energy, and an inductive reactance shunting said crystal holder to supplement the effect of the crystal holder in said circult.

4. In a filter system for filtering modulated wave energy, a reactance energized by said wave energy, an impedance, a series circuit including said impedance and reactance and output terminals, a piezo electric crystal in a holder connected in shunt to said output terminals said crystal in its holder being parallel resonate at substantially the mean frequency of the modu-' lated Wave energy, a second impedance, a second seriescircuit including said second impedance and reactance and another pair of output terminals, a second piezo electric crystal in a holder connected in shunt to said second pair of output terminals, and reactances shunting each of said crystal holders to supplement the effect of the crystal holders in said circuits and thereby control the reactive characteristic of said system.

5. In a filter system for filtering modulated wave energy, a reactance energized by said Wave energy, an impedance, a series circuit including said impedance and reactance and output terminals, a piezo electric crystal in a holder connected in shunt to said output terminals, at

second impedance, a second series circuit including said second impedance and reactance and another pair of output terminals, a second piezo electric crystal in a holder connected in shunt to said second pair of output terminals, and reactances of different character shunting each of said crystal holders to supplement the effect of the crystal holders in said circuits and thereby control the reactive characteristic of said system.

6. In a filter system for converting phase modulated wave energy to characteristic Wave energy and demodulating the same, a reactance energized by said phase modulated Wave energy, an impedance, a series circuit including said impeance and reactance and output terminals, a piezo electric crystal in a holder connected in shunt to said output terminals, a second impedance, a second series circuit including said second impedance and reactance and another pair of output terminals, a second piezo electric crystal in a holder connected in shunt to said second pair of output terminals, an inductive reactance shunting one of said crystal holders, a capacitive reactance shunting the other of said crystal holders, said reactances supplementing the efiect of the crystal holders in said circuits, and rectifying means connected With said output terminals. '7. In a system for converting phase modulations on wave energy to characteristic amplitude modulations and detecting the same, the combination of a detecting circuit, a crystal in a holder, means connecting said crystal and holder in an under-neutralized circuit resonant substantially at the mean frequency of the phase modulated wave energy to be received, a second crystal in a second holder, means connecting said second crystal and second holder in an over-neutralized circuit substantially resonant at the mean frequency of the Wave energy to be received, means for impressing phase modulated Wave energy on said filter circuits, and means for impressing resulting energy from said circuits on said detecting circuit.

8. In a filter system for converting phase modulations on wave energy to characteristic amplitude modulations and detecting the same, the combination of a detecting circuit, a crystal in a holder, impedance means connecting said crystal and holder in a filter circuit resonant substantially at the mean frequency of the phase modulated wave energy to be received, capacitive means connected with said crystal and holder for underneutralizing said filter circuit, a second crystal in a'second holder, impedance means connecting said second crystal and second holder in a filter circuit substantially resonant at the mean frequency of the wave energy to be received, inductive means connected with said second crystal and holder for over-neutralizing said filter circuit, means for impressing phase modulated wave en ergy on said filter circuits, and means for impressing resulting energy from said filter circuits on said detecting circuits.

9. In a system for converting phase modulations on wave energy into characteristic amplitude modulations on Wave energy and demodulating the same, an impedance, a rectifying circuit, a first crystal in a holder, a second crystal in a holder, a first circuit coupling said first crystal to said impedance and to said rectifier circuit for transferring Wave energy to be converted from said impedance to said rectifier circuit, said first circuit including means for over-neutralizing the capacity of the holder of said first crystal, and a second circuit coupling said second crystal to said impedance and to said rectifier system for transferring wave energy from said impedance to said rectifier system, the crystal holder of said second crystal being unneutralized.

10. In a system for converting phase modulations on energy to characteristic amplitude modulations on said wave energy and demodulating the same, a tuned reactance, a rectifying circuit, a first crystal in a holder, a second crystal in a holder, a first circuit coupling said first crystal holder to said tuned reactance and to said rectifier circuit for transferring wave energy to be converted from said impedance to said rectifier circuit, said first circuit including a tuned reactance for over-neutralizing the capacity of the holder of said first crystal, a second circuit coupling said second crystal holder to said tuned reactance and to said rectifier system for transferring wave energy from said tuned reactance to said rectifier system, and a tuned reactance connected to the crystal holder of said second crystal tounderneutralize the same.

11. In a system for demodulating phase modulated wave energy, a reactive circuit tuned substantially to the mean frequency of said phase modulated Wave energy, a detector system, a first crystal in a holder, a second crystal in a holder, impedances connecting each of said crystals in shunt to said reactive circuit, circuits connecting said crystals to said detector system, and reactances of difierent character connected in shunt to each of said crystals.

12. In a system for filtering modulated Wave energy, a reactive circuit tuned substantially to the mean frequency of said wave energy, means for impressing modulated Wave energy on said reactive circuit, a first crystal in a holder, a second crystal in a holder, said crystals in their holders being resonate at substantially the mean frequency of said wave energy, means for varying the airgap of one of said holders, impedances connecting each of said crystals in shunt to said reactive circuit to impress Wave energy to be filtered from said reactive circuit on said crystal, and a reactance connected in shunt to at least one of said crystals to adjust the reactive characteristic of said system.

13. In a system for converting phase modulations on wave energy to characteristic amplitude modulations, demodulating the same and simultaneously suppressing undesired amplitude modulations on said wave energy, a reactance tuned substantially tothe mean frequency of said Wave energy on which said wave energy to be converted may be impressed, a diode rectifier system comprising two rectifiers having their electrodes coupled by a circuit including resistors, said resistors being coupled to a utilization circuit, a first crystal in a crystal holder, a second crystal in a crystal holder, a separate impedance connecting each of said crystals in shunt tosaid reactance, means connecting each of said crystals to said first circuit, a second reactance connected in shunt to one of said crystals, and a third reactance connected in shunt to the other of said crystals.

14. A system as recited in claim 13 wherein said second and third reactances each comprise inductance and capacity, one of which is variable.

15. In a system for converting phase modulations on wave energy to characteristic amplitude modulations, demodulating the same and simultaneously suppressing undesired amplitude modulations on said wave energy, an impedance on which said wave energy to be converted may be impressed, a diode rectifier system comprising two rectifiers having electrodes coupled in push pull relation by a circuit including impedances coupled to a utilization circuit, a first crystal in a crystal holder, a second crystal in a crystal holder, a pair of coupling tubes having input and output electrodes, the output electrodes of said coupling tubes being coupled by band pass filter circuits, resonant at the mean frequency of the Wave energy to be received, to said first circuit, a separate impedance connecting each of said crystals in shunt to said first named impedance, means connecting each of said crystals in shunt with the input electrodes of one of said coupling tubes, and a reactance connected in shunt with at least one of said crystals.

16. In a system for converting phase modulations on wave energy to characteristic amplitude modulations, demodulating the same and simultaneously suppressing undesired amplitude modulations on said wave energy, a tuned reactance on which said Wave energy to be converted may be impressed, a diode rectifier system comprising two rectifiers each having an anode and a cathode, resistors coupling said cathodes together and to a utilization circuit, a first crystal in a crystal holder, a second crystal in a crystal holder, a pair of coupling tubes having input and output electrodes, the output electrodes of each coup-ling tube being coupled by separate band pass filter circuits, resonant at the mean frequency of the wave energy to be received, to the electrodes of said detecting system, an impedance connecting each of said crystals in shunt to said first tuned reactance, means connecting each of said crystals to the input electrodes of a different one of said coupling tubes, an inductive reactance connected in shunt to one of said crystals, and a capacitive reactance connected in shunt to the other of said crystals.

17. In a system for converting phase modulations on wave energy into characteristic amplitude modulated Wave energy and demodulating the same and simultaneously reducing undesired modulations on said wave energy, a reactance on which said wave energy may be impressed, a pair of electron discharge amplifying and coupling tubes having input electrodes and output electrodes, a rectifier system having output electrodes coupled to a utilization circuit and having input electrodes, band pass transformers coupling the output electrodes of said coupling tubes to the input electrodes of said rectifier tubes, a pair of piezo electric crystals each in a holder having two electrodes, means connecting one of said crystals in its holder in series with the input electrodes of one of said coupling tubes in shunt to a portion of said reactance, means connecting the other of said crystals in its holder in series with the input electrodes of the other of said coupling tubes in shunt with another portion of said reactance, and a neutralizing condenser connected in shunt to the holder of one of said crystals, said last shunt connection including a portion of said reactance.

18. In a system for converting phase modulations on wave energy into corresponding amplitude modulations on wave energy, a reactance, means for impressing said wave energy on said reactance, an output circuit on which said converted wave energy may be impressed, a pair of piezo electric crystals in holders having two electrodes, a circuit connecting the electrodes of one of said piezo electric crystal holders in series with a portion of said reactance and coupling the same to said output circuit, a circuit connecting the electrodes of the other of said piezo electric crystal holders in series with a portion of said reactance and coupling the same to said output circuit, and a variable reactance connecting a portion of said first reactance in shunt to the electrodes of at least one of said crystal holders to control the neutralization of the same.

19. In a phase modulation receiver the combination of an output circuit, an under-neutralized crystal resonant substantially at the mean frequency of the phase modulated Wave energy to be received, an over-neutralized crystal resonant substantially at the mean frequency of the wave energy to be received, means connecting each of said crystals in a filter circuit which is reactive in the same sense as to frequencies on opposite sides of the mean frequency of the wave energy to be received, the respective filter circuits being reactive in opposite or opposed senses, means for impressing phase modulated wave energy on said crystals, and differential rectifying means for impressing resulting energy from said crystals to said output circuit.

20. In a phase modulation receiver, a tunable oscillatory circuit for producing oscillator energy to beat with phase modulated wave energy to produce correspondingly modulated energy of lesser frequency, a filter including a crystal in an undermeutralized holder resonant substantially at the mean frequency of said energy of lesser frequency, a filter including a crystal in an over-neutralized holder resonant substantially at the mean frequency of said energy of lesser frequency, means for impressing said energy of lesser frequency on said filters to be passed thereby, means for rectifying the energies passed by said filters to derive the modulation components, and a component which varies in accordance with slow changes in said lesser frequency, and means for controlling the tuning of said tunable circuit in accordance with said last component.

21. In a system for demodulating phase modulated wave energy, a circuit of substantial impedance to wave energy of a frequency of the order of the frequency of the Wave energy to be demodulated, a detector system, a first crystal in a crystal holder, a second crystal in a crystal holder, means connecting each of said crystals in a circuit coupled with said first circuit, means connecting said last circuits to said detector system and a reactance connected in shunt to at least one of said crystals.

22. In a system for demodulating phase modulated Wave energy, an impedance excited by said phase modulated wave ener y, a detector system, a first crystal in a crystal holder, a second crystal in a second crystal holder, means connecting each of said crystals in its holder in a series circuit'coupled with said impedance whereby voltages produced in said impedance by the phase modulated wave energy are impressed on said crystals, means connecting said series circuits to said detector system and a reactance connected in shunt to at least one of said crystals.

23. In a system for demodulating phase modulated Wave energy, a rectifier circuit tuned substantially to the mean frequency of said phase modulated Wave energy, a detector system, a first crystal in a crystal holder, a second crystal in a crystal holder, means for connecting each of said crystals in a series circuit coupled to said rectifier circuit, means connecting said series circuit to said detector system, and reactances of different character connected in shunt to each of said crystals.

MURRAY G. CROSBY. 

